1. Field of the Invention
The present invention relates to a bioabsorbable modified polyester composition mainly used for medical materials, a preparation process thereof and use of the composition.
The main ingredient of the modified polyester of the invention is a polyester containing at least glycolic acid recurring-units and/or lactic acid recurring units, or a polyester containing at least silicone modified glycolic acid recurring units and/or silicone modified lactic acid recurring units.
The present invention also relates to a modified polyester composition which can improve flexibility and softness of bioabsorbable polyester and extend its use for medical materials.
2. Description of the Prior Art
Polyesters represented by polylactic acid (hereinafter abbreviated as PLA), polyglycolic acid (hereinafter abbreviated as PGA) and glycolic acid/lactic acid copolymers (hereinafter abbreviated as PGLA) are interesting bioabsorbable materials. These materials are nonenzymatically hydrolyzed in vivo. The decomposition products, glycolic acid and lactic acid, are finally converted to carbon dioxide and water through a metabolic pathway, and are excreted externally.
For example, high molecular weight PGA is processed into a form of fiber and used for aseptic surgery materials such as sutures and gauzes.
PLA and PGLA are also excellent in processability and solubility in solvents and hence have already been used as the matrix of slow release medicines for intravenous injection by being processed into, for example, microspheres.
Japanese Patent Publication SHO 64-2383(1989) has disclosed that PGLA and PLA are processed into the form of film and used an adhesion inhibitor for curing diseases due to tissue adhesion.
The preparation of polyesters such as PGA, PLA and PGLA is well documented in the literature as exemplified by Polymer, Vol. 20, p1459(1979). The preparation is generally carried out by the ring-opening polymerization of glycolide and/or lactide which are dehydrated cyclic dimers of glycolic acid and latic acid.
A process for preparing polyesters by the dehydrating polycondensation of glycolic acid and/or lactic acid is also disclosed in, for example, Japanese Patent Laid-Open Publication SHO 56-45920(1981).
Polyesters such as PGA, PLA and PGLA are excellent in bioabsorbability and hence utilized in various medical materials.
Recently, it has been further desired to provide flexibility and softness to these polyesters.
For example, PLA and PGLA have a good film-forming ability and have been known to form a tough film by casting a solution of PLA and PGLA. However, these films are stiff and unsuitable for use in vivo, particularly for application to soft tissue.
According to the information of the present inventors, it has been confirmed that even the film of PGLA which is said to be the most flexible becomes stiff by completely removing the solvent remaining in the film after casting.